Radio communication systems utilizing multiplexed noise codes are generally known. A typical example is shown and described in U.S. Pat. No. 4,293,953, entitled, "Bi-Orthogonal PCM Communications System Employing Multiplexed Noise Codes", which issued to Frank S. Gutleber, the present inventor, on Oct. 6, 1981.
The concept of code expansion for the general class of multiplexed noise codes comprised of code mate pairs having autocorrelation functions which upon detection with a matched filter provide an impulse autocorrelation function is also generally known. One known expansion concept involves the butting of one code mate with the other code mate and is a technique disclosed, for example, in U.S. Pat. No. 3,461,451, entitled, "Code Generator To Produce Permutations Of Code Mates", which issued to the present inventor on Aug. 12, 1969.
In the above referenced related application U.S. Ser. No. 499,727 entitled, "Code Generator For Interleaved Multiplexed Noise Codes", there is disclosed a method and apparatus for generating a pair of expanded multiplexed noise codes resulting from interleaving one code mate with the other code mate and is achieved by delaying one of the code mates by a time delay equal to one half the interpulse period of the code mate pairs and adding it to the other code mate to form a first interleaved code mate, while a second interleaved code mate is generated by forming the negative of the delayed code mate and adding it to the other code mate. The interleaved code mates then comprise twice the number of code bits and the process is repeated; however, the code delay is reduced by half for each succeeding interleaving stage. The process can be repeated until the delay is equal to the pulsewidth of each code bit, whereupon a code sequence is provided wherein each available time slot is filled with a code bit.
In the above referenced related application, U.S. Ser. No. 533,183, entitled, "Multilevel Noise Code Mate Pair Generation And Utilization Of Such Codes", there is disclosed a pulse code modulator communications system employing multiplexed noise code mate pairs comprised of a pair of bi-polar digital code mates having more than one amplitude level and employing basic code mate pairs of at least two code bits each wherein one code mate is comprised of two signal bits of first and second polarities with one bit having a larger amplitude than the other bit and wherein the other code mate is comprised of two signal bits of the second polarity and one bit has a larger amplitude than the other bit.
In the above referenced related application U.S. Ser. No. 536,064, entitled, "Expanded Multilevel Noise Code Generator Employing Butting", there is disclosed the concept of the generation of code mate pairs comprising a pair of expanded noise code mates having code portions of more than one amplitude level and which are generated by butting noise code mates of different amplitude levels such that mutually transposed butted code mates in the expanded code mate pairs have respective code bits which are amplified by a predetermined gain factor and wherein one of the butted code mates comprises a complement or negative of one of the original code mates.
Accordingly, it is an object of the present invention to provide an improvement in the generation of noise codes.
Another object of the present invention is to provide an improvement in the generation of multiplexed code mate pairs having more than one amplitude level.
Still another object of the invention is to provide an improvement in the generation of multilevel, multiplexed code mate pairs generated by the process of interleaving code mates.